what is the effect of temperature on pH value?

Answer 1

It's not none whatsoever but it is relatively small if you are talking about relatively simple systems. The link below gives a nice succinct discussion of this.

There is an interesting effect of temperature on pH if the acid is carbonic acid. In this case, increases in temperature will decrease the solubility of the sparingly soluble species. In the case of carbonic acid, it will make the CO2 forming the carbonic acid less soluble so the CO2 concentration in the solution will decrease and pH will rise, in contrast to the discussion in the link below. I realize this isn't really what you asked, you are getting at the effect of temperature on the free energy of the hydronium ion, but I just wanted to point out there are other chemical processes that can go on affecting pH that the thermodynamics of the proton. :-)

Answer 2

I don't think that what the people above are saying is entirely true. I think temperature has an important effect on pH that should be considered.

Think of it this way.

Compounds are made up of bonds. Water molecules too. It takes energy to break those bonds. When energy is added in the form of heat it will break the bonds. In the case of water it will break an O-H bond to give you OH- and H+. So the more energy you add to a system of water the more H+ you will observe. Or the more you heat up water the lower the pH.

Have you ever had to dissolve a compound in water, that is insoluble unless heated? Same thing.

Answer 3

The pH of any solution is a function of its temperature. Voltage output from the electrode changes linearly in relationship to changes in pH, and the temperature of the solution determines the slope of the graph. One pH unit corresponds to 59.16 mV at 25°C, the standard voltage and temperature to which all calibrations are referenced. The electrode voltage decreases to 54.20 mV/pH unit at 0.0°C and increases to 74.04 mV/pH unit at 100.0°C (see graph).

Since pH values are temperature dependent, pH applications require some form of temperature compensation to ensure standardized pH values. Meters and controllers with automatic temperature compensation (ATC) receive a continuous signal from a temperature element and automatically correct the pH value based on the temperature of the solution. Manual temperature compensation requires the user to enter the temperature. ATC is considered to be more practical for most pH applications.
When temperature changes, the actual pH of the solution being measured changes. This change is not an error caused by the change in temperature. It is the true pH of the solution at the new temperature. Since this is not an error, there is no need to correct or compensate for this temperature effect. To be absolutely correct, document both the pH and temperature of the sample...

Answer 4

temperature effects dissociation and solubility, and therefore indirectly affects pH as well.
there is no definite rule how it affects it, it depends on the system you are measuring.
e.g. for pure water, which has a pH of 7 at 25 Celcius, a pH of about 6.6 at 50 celcius and a pH of about 7.5 at 0 celcius.

but a pH 4.0 (25 celsius) buffer has a pH of 4.1 at 60 celsius, (i.e. rise with temperature), while a pH 10.0 (25 celsius) buffer has a pH 9.75 at 60 celsius.(i.e. drops with temperature).

so you see, no general rule how it effects it, but it definitely does.

Answer 5

Since pH is a measure of [H+], there is no effect. However, Kw does increase somewhat with temperature.

Answer 6

None whatsoever.